I am a volunteer on the local fire department so I have emergency lights as well as an alternating flasher on my highbeams. One of my sets of blue lights are attached to the alternating flasher as well to make the patterns more offset so it looks more intense, but to make a long story short when I use my highbeams; 1 highbeam turns on, one turns off, and one of my blue lights comes on.

I was told I needed some sort of diode to prevent the current from coming back into the flasher and messing it up but I'm not really sure what kinda diode to get and how exactly it gets wired up.

Thanks in advance

You should wire the lights sepratly, have two bulbs in the head lights in need be.

I agree, wire the blue lights seperately from the headlights.
This way, you'll avoid issues like this and possibly avoid a costly LCM failure.

Well either way, the left and right high's are connected to eachother so I had to cut one of the wires to get them to alternate with the flasher. The problem isn't that 2 of the blue lights are hooked up through the flasher. Thats another problem cause by the initial problem of preventing the current from traveling backwards into the flasher again.

Like you mentioned a diode is basically a one-way check valve - it lets current flow only in one direction.

You should probably be able to use a 1N4004 diode, very cheap and very common Radio Shack item:
http://www.radioshack.com/product/index.jsp?productId=2036270

It needs to be installed into the wiring between the flasher and the bulb. This will let current flow from but not back to the flasher. Cover the entire thing with shrink tubing.

When I did my HID projector retrofit I used the same diode to keep the bulbs on when the hi beam solenoids were activated.

You shouldn't use a diode in a power wire for 3 reasons:
1) power diodes are expensive
2) power diodes put off a lot of heat, so they can damage the harness or start a fire
3) all diodes create a voltage drop (typically 0.7V) which reduces power to the load (dimmer headlights in this case)

Any diode should be on the control side of the system.

So how exactly should I stop the current from going back the other way?

As I said in the last line of that quote: put the diode(s) on the CONTROL side of relays that turn each headlight on. The power goes thru the relay; the relay needs very little current, and the voltage drop the diode creates isn't enough to affect the relay.

I'm still not 100% sure on what you mean exactly by control side. The relay has a positive and then 2 loads. Do you mean put the diode in line with the power wire coming from battery and into the relay? Because besides that all there is is the direct wires then going to the positive wire for the highbeams.

The diode jumps the two activation pins on the relay with the flow pointing to low beams from high beams.

EDIT: NVM i thought u guys were talking about the upgraded wiring hanress...

A relay has a coil that controls its load switch. The coil has 2 terminals (like most electrical devices), and the load switch uses the other terminals (usually 2 or more, unless it shares a terminal with the coil). The control circuit runs thru the coil. You want 2 ways of controlling the relay: the normal h/l sw., and the wig-wag. You MIGHT need a diode or 2 to isolate the 2 control inputs.

But since you haven't posted the electrical details of your wig-wag, I'm still not sure you even need a diode.

^^^ He is correct about using the diode in the control side. When I posted earlier I forgot to mention that. Look at the wiring diagram I showed - you will see that the diode is connected to wires from the harness plug going to terminal 86 of the different relays.

That is the terminal that energizes the relays, meaning that is what is controlling the relays - that's the control side that's mentioned. It only takes milli-amps to energize a relay so diode can be safely installed.

The actual amperage load comes from the battery to terminal 30 of the relays and is protected by using a circuit breaker. When terminal 86 gets power, that energizes the relay. This in turn closes an internal contact and sends the power at terminal 30 out from terminal 87. Amperage load is never sent thru any switches or diodes, just thru the relay. Very safe and ensures minimal resistance (equals heat) and loss of voltage/amperage.

That's essentially what the headlight relay harness upgrade kits do.

Should I have hooked it up differently in the first place? lol.

How could we know? You haven't posted a wiring diagram or even a detailed description of how you hooked it up to begin with. But after re-reading your first post, I don't think a diode will solve your problem. I think it's just wired wrong, and the high beams are never switching back to "normal". They just don't flash when you use the stock high-beam switch.

BTW
The diode in Blue95's diagram serves a totally different purpose. It allows the high-beam output from the switch to continue energizing the HID ballasts, but prevents the low-beam output from backfeeding to the high-beam solenoid. It's a peculiarity of an HID system that physically moves the bulbs to change the aim of the beams.

Slight clarification - not all HID projectors move the bulbs. In my case, the E55's are equipped with the solenoid that controls a flap in front of the bulbs. Bulb is stationary, solenoid activates to move the flap for hi beams. I only mention this because it's a bit less costly to change the solenoid rather than the bulb holder assembly if replacement is needed.

Steve is exactly correct on the purpose of the diode. Without it, the lights would turn off when the hi-beams are selected.

I also think he is right about the wig-wags, wiring - without diagram or anything cannot diagnose.